Effect of borax on the thermal and mechanical properties of ethylene-propylene-diene terpolymer rubber-based heat insulator

The effect of Borax on the mechanical and ablation properties of three different ethylene-propylene-diene terpolymer (EPDM) compounds containing 20 phr carbon fiber, 20 phr Kevlar or 10 phr/ 10 phr carbon fiber/ Kevlar was investigated. All formulations contained 30 phr fumed silica powder and 10 phr paraffinic oil. It was found that adding Borax to the composite samples containing carbon fiber or Kevlar fiber or their mixture with an equal ratio can increase the tensile strength, elastic modulus and hardness with a slightly decrease in the elongation at break of the rubber samples. The results of thermogravimetry analysis (TGA) on the various samples showed significant increase in the char yield at 670 degrees C by adding Borax to the rubber compounds. Moreover, ablation resistance of samples was also improved by increasing Borax content. Meanwhile, density and thermal conductivity of the insulator were also reduced up to about 10% when the carbon fiber was replaced with the Borax. The results indicated that composites containing Kevlar have high storage modulus and produce compact and stable char. EPDM rubber composite containing Borax (20 phr), carbon fiber (10 phr), and Kevlar (10 phr) showed thermal and ablative properties comparable with those of the asbestos- filled EPDM. The thermal conductivity and ablation rate of the above- mentioned sample were 0.287 W/m/K and 0.13 mm/s respectively. (c) 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41936.